B. Christophe

Bioluminescence and luminescent fish in the Strait of Messina from the mesoscaph “Forel”

Light irradiance was measured at 430, 470 and 500 nm aboard the mesoscaph “Forel” in the Strait of Messina from the surface to 550 m depth in May 1979. The underwater light regime is partly due to the downwelling residual sunlight and partly to bioluminescence. An intense bioluminescence is localized at about 450 m at midday and moves upwards in the evening to reach an area extending from 100 m depth to the surface late in the evening. Two types of luminescence were observed: one associated with luminescent organisms and another diffuse, probably due to bacteria. Three types of luminescent fish were recognized, namely Argyropelecus hemigymnus, myctophids and Cyclothone braueri, and their time and space distribution were studied. While myctophids were encountered from the surface (21:00 hrs) to 550 m depth (16:00 hrs), A. hemigymnus were only observed between 180 m (19:45 hrs) and 500 m (12:15 hrs), and C. braueri between 330 m (16:00 hrs) and 500 m (19:00 hrs). The results do not show a significant relation between the absolute ambient light intensity and the time or the depth where the fish were observed.

The Adrenergic Control of the Photocyte Luminescence of the Porichthys Photophore

1. 1. The isolated photophore or photocytes of Porichthys notatus developed fast and/or slow luminescence in response to stimulation by adrenergie agonists (norepinephrine, epinephrine, isoproterenol, phenylephrine; 1 nM to 1 mM). 2. 2. The isolated photophore and isolated photocytes showed different specific dose-response curves. 3. 3. The α-adrenergic antagonist phenotalamine blocks partially or completely (1) the fast luminescence of photophore and photocytes and (2) the slow luminescence of the photophore. 4. 4. The specificity of the agonist effects and action of phentolamine suggest that α-receptors are associated with neural structures present in the photophore and α- and β-receptors with photocytes. 5. 5. The amplitude of the luminescent response of the photophore is taken to be the sum of the light emitted by the photocytes directly and indirectly stimulated by endogenous and exogenous catecholamines.

Luminescence of Argyropelecus Photophores Electrically Stimulated

Abstract o 1. Isolated photophores of the living bathypelagic fish Argyropelecus hemigymnus respond to a strong (25–80 V) and long (4–15 msec) electrical stimulus by a brief flash emission (F response). 2. Weaker and shorter stimuli are subthreshold, but when repeated at a frequency equal to or higher than one per second, the photophores respond by a slow light emission (S response); it is characterized by a long emission latency time, at least 2 sec duration and by a progressive increase in the rate of light production during the stimulation period. The maximal amplitude of the response is more than 300 times lower than the response of the photophore of the epipelagic luminescent fish Porichthys. 3. A train of strong (35V) and long stimuli (4 msec) applied at high frequency (100/sec) quench temporarily the luminescence of spontaneous luminescent photophores. The inhibitory response is reversible: after the end of stimulation, the light production returns to the level recorded before the stimulation. 4. The inhibitory response to electrical stimulation is tentatively explained either by the presence of an inhibitory nervous system or by the liberation of an excess of adrenalin, the possible natural neuromediator that inhibits luminescence of isolated photophores at high concentration.

Luminescence of isolated photophores and supracaudal gland from myctophum punctatum: Electrical stimulation

Abstract 1. 1. Isolated photophores of the living bathypelagic fish Myctophum punctatum respond to train of weak (10–25 V) and short (2–5 msec) electrical stimuli applied at different frequencies (8–100/sec) by a luminus response. 2. 2. This response is characterized by a short emission latency time, the peak of light develops within about 2 sec after the beginning of the electrical stimulation: afterwards the light decreases to a constant level within about 8 sec. 3. 3. Stimuli of higher strength (60–75 V) and longer duration (8–16 msec) applied at different rates (1–100/sec) evoke brief flashes. 4. 4. The isolated supracaudal gland emits flashes in response to electrical stimulation whatever the strength and the duration of stimuli. 5. 5. The flash of the supracaudal gland differs from the flash of the isolated photophores in three respects: lower threshold, higher magnitude and longer duration.

Luminescence of Chauliodus photophores by electrical stimulation

Abstract 1. 1. Photophores isolated from living specimens of the bathypelagic fish Chauliodus sloanei emit bright flashes or luminus when they are electrically stimulated. 2. 2. Anodic stimuli of long duration (4–8 msec) and high strength (50 V) evoke quick flashes (10–130 10 6 quanta/sec) that fuse in a erratic way when the frequency of stimuli is higher than 2/sec. 3. 3. Anodic stimuli of short duration (1 msec) and low strength (10 V) evoke slow flashes that fuse together in a “luminus” when the frequency of stimuli increases up to 4/sec. 4. 4. The “luminus” response is characterized by a peak of light developed within 2 sec after the beginning of the electrical stimulation; afterwards, the light decreases to reach a constant level of light within about 10 sec.